Small Craft Advisory 818, NWS Anchorage, AK

Southcentral and Southwest Alaska Forecast Discussion
National Weather Service Anchorage AK
411 PM AKDT MON OCT 17 2016

.ANALYSIS AND UPPER LEVELS...
An elongated upper level low centered near Shelikof Strait is
moving southwestward as a short-wave digs southward across the
eastern Bering Sea. Arctic air behind this short-wave is
advecting across Southwest Alaska and over the warm waters of the
Eastern Bering Sea. This is leading to bands of showers and gusty
northerly winds. Precip-type is mostly rain, though expect a
transition toward snow as progressively colder air continues to
advect southward.

On the east side of the upper low center a short-wave trough is
rotating northwestward toward Southcentral, with precip spreading
onshore across Prince William Sound. A surface low is tracking
westward across the southern Kenai Peninsula helping to produce
periods of snow over the southwest Kenai Peninsula, including the
Homer area. Warm air advection behind the surface low and with
the upper trough is leading to a changeover from snow to rain
across the eastern Kenai Peninsula.

&&

.MODEL DISCUSSION...
Models continue to struggle with track of deepening surface low
south of Kodiak Island on Tuesday, though solutions are getting
closer each model cycle. Will trend heavily toward the ECMWF
solution, which has support from Canadian as well as the 18Z NAM.
Even though forecast confidence near the low center is low,
confidence is much higher north of the low center with good
agreement on frontal position and strength. Models all then
develop one or more triple point lows over the Gulf Tuesday Night,
with a very large spread in positions. Thus, forecast confidence
is very low, especially over the Gulf.

&&

.AVIATION...
PANC...VFR conditions will persist through the TAF period. There
will likely be a couple short periods of sub-6000 ft ceilings late
this afternoon and evening as bands of showers transit the area,
though it is difficult to nail down the exact timing.

&&

.SHORT TERM FORECAST SOUTHCENTRAL ALASKA (Days 1 and 2)...
Rain, snow and gusty winds are the challenges into mid week. The
general trend will be diminishing winds tonight across the
Matanuska Valley with a strong short wave bringing increased
precipitation chances across Southcentral, western Gulf and Cook
Inlet. The next front will bring rain and gusty winds along the
Gulf and surrounding coast Tuesday into Wednesday with drier
conditions inland as the associated low tracks south of the coast.

A re-enforcing low in the northern Gulf will initiate rain and
snow showers along the coast this evening with scattered snow activity
moving inland overnight. The Kenai will see a mix of rain and
snow as low pressure moves across the peninsula toward the
Aleutian Range overnight. Temperatures along the Kenai coast are
expected to warm above freezing Tuesday afternoon as a warm surge
moves into the Gulf. This front moves into the southern Gulf
early Tuesday bringing widespread gusty gale winds and rain. Winds
were adjusted across the gulf to bring the boundary across faster
than the previously forecasted. There is still some uncertainty on
the the strength and placement of the low center Tuesday evening
into Wednesday. Winds are the primary challenge during this
timeframe and should be monitored as they may need to be increased
across the Gulf and along the Kenai in future updates.

&&

.SHORT TERM FORECAST SOUTHWEST ALASKA (Days 1 and 2)...
Cool, dry north to northeasterly flow will continue across
southwest Alaska through Tuesday afternoon, as an upper level
trough over mainland Alaska rotates across southwest Alaska and
Bristol Bay to become centered over the Alaska Peninsula and
Kodiak Island this evening. The upper level low will remain in
that general location through Tuesday morning and then drop south
as a surface low rotates north into the Gulf just south of Kodiak
Island then swings west towards the Alaska Peninsula. A low
approaching Kodiak island Tuesday night will bring in some
slightly warmer temperatures and precipitation along the eastern
parts of the Bristol Bay zone. However, there remains some
uncertainty between the models regarding the strength and track of
this system through Wednesday night.

&&

.SHORT TERM FORECAST BERING SEA/ALEUTIANS (Days 1 and 2)...
The surface low south of the central Aleutians will continue east
tonight before tracking into the southwest Gulf by Tuesday. Upper
level ridging will build into the western and central Bering
behind this low continuing northerly flow over the eastern Bering
and Alaska Peninsula through midweek. The next surface low and
associated front will reach the western Aleutians Tuesday night
and track into the central Aleutians/Bering by Wednesday
afternoon.

&&

.LONG TERM FORECAST (Days 3 through 7)...
There are several features moving through the area Wednesday night
into Thursday that look to have an impact for the southern
mainland and Aleutians. The first is a low south of the Gulf that
is bringing easterly winds to the Gulf and rain to the north Gulf
coast. In the coastal ranges it will be cold enough for snow. That
low will then track off to the east.

The second feature is a shortwave tracking southeast across the
southern Bering that looks to bring rain to the Central and
Eastern Aleutians Thursday before moving out into the North
Pacific. The third features is a trough that is digging down
across the state that will make it over Southcentral Alaska
Friday. It will bring another push of cold air, but it looks too
dry to bring much, if any, snow.

Moving towards the weekend, the models fall apart. The main thing
they agree on is that a fairly deep low will move into the western
Bering Sunday. However, there is low confidence for this timeframe
with how much the models are struggling. Ensembles were preferred
over the deterministic solutions.

&&

.AFC WATCHES/WARNINGS/ADVISORIES...
PUBLIC...None.
MARINE...Gale 119 120 130-138 150-165 172 181.

&&

SYNOPSIS AND MODEL DISCUSSION...SEB
SOUTHCENTRAL ALASKA...KH
SOUTHWEST ALASKA/BERING SEA/ALEUTIANS...TP
LONG TERM...DK